1. Field of the Invention
The present invention generally relates to short-range communication, and more particularly, to a method for operating beacons.
2. Description of the Related Art
A Personal Area Network (PAN), in concept similar to the well known Local Area Network (LAN) or Wide Area Network (WAN), is a unique network owned by an individual. That is, terminals owned by one person form a network for the convenience of that person. The concept of forming a PAN in a wireless manner is referred to as a Wireless Personal Area Network (WPAN).
In an effort to implement PAN in a wireless manner, the Institute of Electrical and Electronics Engineers (IEEE) 802.15 Working Group has defined WPAN as a standard of a short-range wireless network. The IEEE 802.15 Working Group has worked for the IEEE 802.15.1 standard known as Bluetooth®, the IEEE 802.15.3 and IEEE 802.15.3a standards associated with high-rate WPANs, and the IEEE 802.15.4 standard known as ZigBee. In particular, the 802.15.6 TG6 is working to standardize Wireless Body Area Network (WBAN) for providing a medical service such as telemedicine and an entertainment service, using equipment or a motion sensor, for wearable computing, through a nearby communication network, within 3 meters from a human body.
FIG. 1 is a conceptual diagram, which illustrates a general structure of a WBAN, where an individual forms a network, that is, a piconet. The piconet includes a coordinator terminal 10, such as a mobile communication terminal, and a plurality of participating terminals 11, 12, 13, and 14, such as various types of peripheral devices or sensors attached to a human body. Since the WBAN is targeted for a device small in size and a mobile power source, such as a sensor with poor power conditions, low power consumption is the most critical system requirement.
FIG. 2 is a diagram illustrating a structure of a super-frame 20 used in a conventional short-range communication system, which includes a beacon (B) 21, a Contention Access Period (CAP) 22, a Contention Free Period (CFP) 23, and an inactive period 24. The conventional super-frame 20 is provided from the coordinator terminal 10 of FIG. 1 to the participating terminals 11 through 14 of FIG. 1. The beacon 21 provides sync reference time to the participating terminals 11 through 14 of FIG. 1, status of the piconet and the status of resource allocation. In the contention access period 22, the participating terminals 11 through 14 of FIG. 1 transmit requests for joining or leaving the network, requests for resource allocation, requests for connection, and requests for authentication to the coordinator terminal 10 of FIG. 1 based on contention access, and the coordinator terminal 10 of FIG. 1 responds to the requests of the participating terminals 11 through 14 of FIG. 1. In the contention free period 23, the coordinator terminal 10 of FIG. 1 and the participating terminals 11 through 14 of FIG. 1 communicate by using allocated resources (e.g., time slots).
In a short-range communication system, which performs communication by using the above-described super-frame, if a beacon is not transmitted to the participating terminals 11 through 14, the system performance abruptly degrades. Therefore, the beacon requires a design that is more robust to a channel condition than a general data message, and also needs a strong modulation and coding scheme according to system conditions. In a personally tailored communication system such as a WBAN, data security is a major consideration. Consequently, the beacon should be encrypted.
Moreover, when a single beacon is used in a super-frame and a large number of participating terminals are connected to the coordinator terminal, the participating terminals may demand various communication environments. As a result, the beacon design must take into account the requirements of all the participating terminals, to avoid causing unnecessary performance degradation of the participating terminals. In particular, a WBAN requiring low power consumption undergoes significant degradation in efficiency and stability.